1. Field of the Invention
The present invention relates generally to the drilling and completion of wells drilled into the earth for the recovery of hydrocarbons. More specifically, the present invention relates to tools used to prevent spillage of well drilling fluids from the fluid circulating system of a top drive of a drilling rig while maintaining the ability to quickly reestablish forward circulation of fluids through the system when necessary.
2. Description of the Background Setting
Casing installed in subsea completions and casing installed as a liner in land and subsea completions is positioned within the well with a landing string, typically a drill string, which has a smaller internal diameter than that of the casing. The use of a landing string is necessary for liners and subsea wells because the casing strings do not extend back to the well surface. As the casing is being lowered into the well, an automatic valve at the bottom of the casing opens to permit well fluids in the wellbore to flow into and fill the casing. Unless the pipe is lowered very slowly, a reverse flow of drilling fluids is induced through the smaller diameter drill string being used to install the casing. Special measures must be taken to confine any reverse flow of drilling fluid from the drill pipe at the well surface.
Drilling rigs that are equipped with top drives can contain the back flow by making up the threaded end of the top drive into each joint or stand of drill pipe as the pipe is being run into the well. The requirement to repeatedly make up and disengage the top drive threads, however, is time consuming and therefore expensive, particularly in offshore installations.
One prior art drill pipe fill up tool for top drives permits drilling mud to back flow through the top drive and associated piping into the rig""s mud pits. The fill up tool slides into the top of the drill string and seals with the drill string to contain displaced fluid as the string is being lowered. The prior art system permits rapid lowering of the drill string without danger of spilling the overflow onto the rig floor. However, while the prior art fill up tool contains the back flow of drilling fluid as the string is being lowered into the well, once the drill string is suspended from slips on the rig floor and the fill up tool is withdrawn from the top of the drill pipe string, the fluid in the top drive and associated flexible piping is freed to flow out onto the rig floor.
A tool connected to the end of the rig""s top drive is provided with a check valve assembly that opens to permit drilling fluid to flow in reverse through the drill pipe as the drill string and casing string are being lowered into the wellbore. The check valve closes to prevent drainage or forward fluid flow from the top drive and associated piping to prevent fluid spillage onto the rig floor when the top drive is disconnected from the drill string. The check valve assembly may be pressure activated by initiating pumping in the circulating system to overcome a spring bias to thereby enable high-pressure flow in the forward-checked direction. The check valve thus functions to permit reverse flow as required to fill the casing, prevents spillage onto the drilling rig floor when the top drive is extracted from the drill string and permits forward fluid flow as necessary to establish circulation when the top drive is connected to the drill string.
Accordingly, it will be appreciated that a general object of the present invention is to provide a tool for preventing spillage of fluids from a drilling rig system used to position well pipe in a well.
Another object to the present invention is to provide a tool for automatically permitting either reverse flow or forward circulation flow of fluid through a well string as a function of the pressure of the fluid acting across the tool.
A specific object of the present invention is to provide a tool for use in a top drive drilling system that accommodates return flow of well fluids from a casing string being installed with a drill string and that prevents leakage of fluid from the top drive and associated piping when the top drive is separated from the drill string while selectively permitting forward pumping circulation through the top drive and drill string as the drill string and casing are being lowered into the well.
It is also an object of the present invention to provide a fill up tool that permits the safe running of subsea completion strings and casing liners from drilling rigs using a top drive unit while maintaining minimal drilling fluid loss and greatly reducing adverse environmental impact.
The foregoing objects, features and advantages of the present invention, as well as others, will be more fully understood and better appreciated by reference to the following specification and claims.